The Lesson of the Kaibab
Introduction:
The environment may be altered by forces within the biotic community, as
well as by relationships between organisms and the abiotic factors in their
environment. The carrying capacity of an ecosystem is the maximum number
of organisms that an area can support on a sustained basis. Population
density is the number of organisms occupying a specific measure of land.
High population density is limited by factors such as increases in competition for resources, predation,
and transmission of parasites and disease. High population density may produce such profound changes
in the environment that the environment no longer has the resources needed by a particular population,
or populations. For instance, overgrazing of land by herbivores may change the amount of resources
available, thus changing the number of grazing of animals that can live there. Other factors, regardless
of the population density, can impact the carrying capacity. Human disturbance and climate extremes
can affect population size no matter how many organisms live there.
Objectives:
 Graph data on the Kaibab deer population of Arizona from 1905 to 1939
 Determine density-dependent and density-independent factors responsible for changing the
deer population size on the Kaibab
 Analyze the reasons for changes in the carrying capacity of the Kaibab Plateau
Background:
Before 1905, the deer on the Kaibab Plateau were estimated to number about 4,000. The average
carrying capacity of the range was then estimated to be about 30,000 deer. On November 28th, 1906,
President Theodore Roosevelt created the Grand Canyon National Game Preserve to protect the "finest
deer herd in America."
Unfortunately, by this time the Kaibab forest area had already been overgrazed by sheep, cattle, and
horses. Most of the tall grasses had been eliminated. The first step to protect the deer was to ban all
hunting. In addition, in 1907, The Forest Service tried to exterminate the predators of the deer. Between
1907 and 1939, 816 mountain lions, 20 wolves, 7388 coyotes and more than 500 bobcats were killed.
Signs that the deer population was out of control began to appear as early as 1920 - the range was
beginning to deteriorate rapidly. The Forest Service reduced the number of livestock grazing permits. By
1923, the deer were reported to be on the verge of starvation and the range conditions were described
as "deplorable."
The Kaibab Deer Investigating Committee recommended that all livestock not owned by local residents
be immediately removed from the range and that the number of deer be cut in half as quickly as
possible. Hunting was reopened, and during the fall of 1924, 675 deer were killed by hunters. However,
these deer represented only one-tenth the number of deer that had been born that spring. Over the
next two winters, it is estimated that 60,000 deer starved to death.
Today, the Arizona Game Commission carefully manages the Kaibab area with regulations geared to
specific local needs. Hunting permits are issued to keep the deer in balance with their range. Predators
are protected to help keep herds in balance with food supplies. Tragic winter losses can be balanced by
keeping the number of deer near the carrying capacity of the range.
Name:
Period:
Date:
The Lesson of the Kaibab
DATA:
1. Graph the deer population data. Place time on the X axis and "number of deer" on the Y axis. Space your years
in appropriate intervals. Note that the deer population was not recorded every year.
Kaibab Deer Population from 1905-1939
1905
4,000
1927
37,000
1910
9,000
1928
35,000
1915
25,000
1929
30,000
1920
65,000
1930
25,000
1924
100,000
1931
20,000
1925
60,000
1935
18,000
1926
40,000
1939
10,000
Analysis:
1. During 1906 and 1907, what two methods did the Forest Service use to protect the Kaibab deer?
2. Were these methods successful? Use the data from your graph to support your answer.
3. Why do you suppose the population of deer declined in 1925, although the eliminated of predators occurred?
4. What density-dependent factors influenced the deer population size on the Kaibab Plateau?
5. What density-independent factors influenced the deer population size on the Kaibab Plateau?
6. Why did the deer population decline after 1924?
7. Based on these lessons, suggest what YOU would have done in the following years to manage deer herds.
1915:
1923:
8. Humans are still hard at work monitoring and balancing the Kaibab deer population. What has to happen in
order for that ecosystem to function without human intervention?